Breaching the Finger Biscuit Fortress – Milk Mustache

Ingredients

• 225 g flour
• 1 tbsp double acting baking powder
• ½ tsp baking soda
• ½ tsp salt
• 400 g (2 cups, 14 oz) golden caster sugar
• 2 large eggs, at room temperature
• 115g (4 oz, 1 stick) unsalted butter, at room temperature, cut into cubes
• 70 g (½ cup + 2 tbsp)cocoa powder
• ½ cup (120ml) buttermilk
• 1 cup (240 ml) water
• 2 tsp natural vanilla extract
• 170 g (1½ cups, 6 oz) powdered sugar
• 2 tbsp cocoa powder
• 35 g (1⅙ oz, 2½ tbsp) unsalted butter, at room temperature
• 2 - 3 tbsp sour cream
• 3 tsp natural vanilla extract
• Pinch of salt
• 100 g dark (min. 70% cocoa solids) chocolate
• 50 g unsalted butter
• 1 pack each of Cadbury's dark, milk and white chocolate finger biscuits
• 20 - 30 g finely chopped chocolate (I used white)